AUTOMATED DIBUCAINE NUMBER MEASUREMENT WITH DUPONT DIMENSION(R) ES AND AR ANALYZERS

We report a fully automated method for determining dibucaine number (D N) in a single-run procedure involving Dimension(R) cholinesterase (CH E) Flex(TM) pseudo-(P)CHE reagents. The method was developed and optim ized with the ''open channels'' and ''kinetic'' software facilities of the Dimension-ES instrument, where the DN is calculated automatically by an algorithm from the ratio of the uninhibited and inhibited rates , measured bichromatically, from a single analysis. The protocol was s atisfactorily assessed for substrate depletion, linearity, reagent sta bility, and the effects of different dibucaine concentrations. Validat ion was performed across a range of CHE activities (1.5-22 kU/L) repre senting the three main genotypes, UU, UA, and AA. The respective DNs ( mean +/- SD), determined on the Dimension-ES, were 82.0 +/- 1.6 (n = 3 2), 71.0 +/- 3.1 (n = 10), and 23.0 +/- 2.7 (n = 14), with correspondi ng imprecisions (CV) of 0.3%, 0.6%, and 5.2% (intraassay) and 0.7%, 0. 7%, and 8.6% (interassay). Comparisons with reference (x) laboratory v alues and the DuPont aca(R) (X') procedure (n = 53) gave regression eq uations of: y = 0.88x + 11.2, r = 0.99, and y = 0.85x' + 11.9, r = 0.9 9. A separate trial conducted with a Dimension-AR instrument gave simi lar performances. We conclude that the new DN method is fast, efficien t, and appropriate for clinical use.